1. Field of the Invention
The present invention relates to a combined oil ring utilized in internal combustion engines, and relates in particular to a combined oil ring with low oil consumption.
2. Description of the Related Art
A compression ring functioning mainly as a gas seal; and an oil control ring functioning mainly to control the thickness of the oil film on the wall surface of the cylinder bore are mounted on a piston in an internal combustion engine. The oil control ring is mainly a steel combined oil ring with a spacer expander and separate upper and lower rails; or a steel combined oil ring with an integrated upper and lower rail structure and having a coil expander. These oil control rings control the thickness of the oil film on the cylinder wall by pressing the rail section against the inner wall surface of the cylinder bore by the expander to scrape off oil on the inner wall surface of the cylinder bore.
In the case of the combined oil ring with an integrated upper and lower rail structure, oil loss occurs via the gap because the gap positions on the upper and lower rails are at the same or nearby positions along the periphery. In other words, the oil mist that passed through the gap of the lower rail and the oil remaining on the cylinder wall due to the gap of the lower rail tend to easily pass through the gap of the upper rail and enter the combustion chamber. This oil loss phenomenon is particularly drastic when the gaps of the upper and lower rails are aligned with each other since the combustion chamber reaches a negative pressure during deceleration where there is an engine braking effect. Also, the sealing on the upper side of the piston ring groove is weak in the combined oil rings with an integrated upper and lower rail structure so that oil loss occurs in the clearance between the upper surface of the ring groove and the upper surface of the oil ring. This oil loss phenomenon becomes especially drastic during deceleration where engine braking occurs, because the combustion chamber reaches a negative pressure.
Technology for preventing oil loss due to pumping effect is described in Japanese Patent Non-examined Publication No. 50-94311 for a combined oil ring in which a belleville spring contacting the upper surface of the oil ring and the upper surface of the ring groove is mounted on the upper side of the oil ring. Technology for preventing oil loss during high loads is described in Japanese Patent Non-examined Publication No. 4-88261 for a combined oil ring with low tensile force and thin width in which side rails are mounted above and below the spacer expander, the bottom surface of the spacer expander is flat, and the side rail on the lower side acts no radial force substantially. Technology for providing a high tensile force on the upper and lower surfaces of the ring groove and the inner circumferential surface of the cylinder, and high conformability on the inner circumferential surface of the cylinder is described in Japanese Patent Non-examined Publication No. 5-231540 for a combined oil ring in which side rails are mounted at the top and bottom of the support ring, and a coil expander is mounted on the inner circumferential side of the support ring.
The technology disclosed in Japanese Patent Non-examined Publication No. 50-94311 has the problem that the belleville spring restricts the oil ring and impedes the oil ring movement, which is sometimes a factor causing oil consumption to worsen. The technology disclosed in Japanese Patent Non-examined Publication No. 4-88261 and Japanese Patent Non-examined Publication No. 5-231540 contains no oil ring having upper and lower rails formed integrally at the outer circumferential side of the oil ring to slide on the cylinder wall. Moreover, the side rail on the upper side is pressed against the upper surface of the ring groove so that poor conformability of the upper side rail on the inner circumferential surface of the cylinder due to carbon sludge deposits, as well as wear at the contact portion between the side rail pressing section and the side rail sometimes inhibit the oil control function.